Old Light, But New to Us...
Now let's examine the nature of this microwave background. Because
was released everywhere at once, it is all around us. This light was created
by a very unique event, so fortunately it has a very specific energy distribution
that makes it easy to identify, similar to a fingerprint. That is, it is
easy to see once you know what you're looking for.
The Anisotropy of the Microwave Background
The cosmic microwave background was actually discovered by accident in 1964
by Arno Penzias and Robert Wilson of Bell Laboratories. They were trying
to eliminate static interfering with radio
experiments. They tuned out local radio stations and even built pigeon traps
to rid themselves of birds nesting in and around their radio receiver, because
the pigeon droppings were a strong source of static.
Despite their best efforts, Penzias and Wilson couldn't eliminate a constant low-level noise. They came to realize (after a good deal of iteration with cosmologists at Princeton University) that this noise has been lingering for 10 billion to 15 billion years, predicted by the Big Bang theory. They won the 1978 Nobel Prize for it.
COBE was the first satellite
to study the cosmic microwave fossil. In 1992, COBE found that there were
slight temperature differences in this evenly spread blanket of light. The
Universe has cooled down considerably since its early days. Even with the multitude of stars,
the microwave background only averages 2.78 degrees above absolute zero.
The temperature differences are less than ten-thousandth of degree from
region to region.
The temperature variations in the cosmic
as detected across the sky by COBE.
What do these temperature differences mean? The temperature differences, or fluctuations, we see today point back to density
differences in the early Universe. Certain regions were denser and hotter
than other regions, however slight. But you have no doubt heard the expression
"give an inch and they'll take a mile." The slight differences in density
were the seeds that grew into galaxies and galaxy clusters.
Through the force of gravity, dense regions pulled in more and more matter, even as the Universe expanded. The more massive
they became, the more matter they could attract through gravity. Less dense
regions did not grow. It's the old story of the rich get richer. Those
early, dense regions accumulated enough matter to form stars and galaxies.
Less dense regions evolved into modern regions of seemingly empty space,
The precise temperature fluctuations in the microwave
background from region to region speak specifically about how this modern
structure formed. The development depended on the shape of the Universe
and the type and amount of matter and forces that exist. Different shapes
and different amounts of matter would leave their marks as different temperature
fluctuations from region to region.
COBE had a resolution of about 7°, just enough to provide a fuzzy picture
of the temperature fluctuations. MAP will have 35 times better resolution,
enabling scientists to study the microwave background at the smallest angular
The temperature variation in the
microwave background as its expected to be seen by MAP.